In the drilling of oil and gas wells, a drill bit attached to the bottom of a drill string bores a hole into underground formations. A drill string typically comprises a long string of connected drill pipe sections that extend from the surface into a well bore formed by the drill bit on the bottom of the drill string. Casing is typically installed at various depths throughout the well bore from the surface to prevent the wall of the bore from caving in; to prevent the transfer of fluids from the various drilled formations from entering into the well bore, and visa versa; and to provide a means for recovering petroleum if the well is found to be productive.
During rotary drilling operations, the drill pipe is subjected to shock and abrasion whenever the drill pipe comes into contact with the walls of the well bore or the casing itself. In many drilling operations, the drill pipe may extend underground along a curved path, rather than extending vertically; and in these instances a considerable amount of torque can be induced by the effects of the frictional forces developed as a result of the rotating drill pipe with its protectors coming into contact with the casing or the wall of the well bore.
In the past, drill pipe protectors have been placed in different locations along the length of the drill pipe to keep the drill pipe and its connections away from the walls of the casing and/or formation. These drill pipe protectors have been typically made from rubber or other elastomeric materials because of their ability to absorb shock and impart minimal wear. Typical prior art drill protectors are shown in U.S. Pat. Nos. 4,796,670 Russell, et al.; 4,266,578-Swain, et al.; and 3,480,094 typically solid rubber protectors having an outside diameter (O.D.) greater than that of the drill pipe tool joints, and these protectors are typically installed or clamped rigidly onto the O.D. of the drill pipe at a point near the tool joint or the connection of each length of drill pipe. Such an installation allows the rubber protector only to rub against the inside wall of the casing as the drill pipe is rotated. Although wear protection for the casing is the paramount result when using such drill pipe protectors, they can produce a significant increase in the rotary torque developed during drilling operations. The problem that prevails is that current protectors (there can be hundreds of these protectors in the well bore at any one time) can generate sufficient cumulative torque or drag at a radius sufficient to effectively curtail drilling operations if the power required to rotate the drill pipe approaches or exceeds the supply power available. An additional problem occurs when the drill pipe begins failing in torsion due to the high levels of torque produced in response to the drag generated by the current drill pipe protectors.
In the past, the problems of wear protection for the casing along with torque build-up have been addressed through improvements directed toward producing drill pipe/casing protectors from various low friction materials in different configurations. To date experience has shown that these techniques have only been marginally effective, and oil companies are still searching for effective means to greatly reduce the wear and frictionally developed torque normally experienced when drilling deeper wells and directional wells, including horizontal well bores.